103 
PLEUROTOMA. Lam. 
Gen. Char. An univalve, fusiform or subturreted 
shell ; base of the aperture channelled ; a deep 
sinus in the upper part of the outer lip, 
The form of the mouth ill fossil shells of this Genus is 
seldom distinguishable except in the lines of growth ; the 
thinness of the outer lip renders it so liable to accidents. 
The general form is similar to that of Murex, Fusus, 
&c. The beak is straight, and the columella without 
plaits. 
PLEUROTOMA attenuafa* 
TAB. CXLVl.—Fig. 1. 
Spec. Char. Fusiform, base attenuated ; longitu- 
dinally undulated ; undulations five or six, with 
a large compressed tubercle at the upper end 
of each ; volutions transversely striated ; aper- 
ture narrow, straight. 
The upper part of each whorl is nearly even, being only 
striated and is bounded by transversely compressed tuber- 
cles on the upper part of oblique undulations or costae ; 
over these and the remainder of the whorl are numerous 
small subtuberculated ridges with stria? between them,, 
The aperture equals half the entire length of the shell : 
the beak is produced by the gradual tapering of the last 
whorl and is of the same length as the spire ; the width 
is equal to one fourth of the length ; a rugged aspect is 
given by the irregular lines of growth. 
This species seems to be rare, I have only yet seen two 
pieces, found at Stubbington by Mr. Holloway. Although 
many species from that place agree with those found at 
Highgate and Barton, and the foreign ones 5 yet I believe 
this is found no where else. 
